Gd and Eu Co-Doped Nanoscale Metal–Organic Framework as a T(1)–T(2) Dual-Modal Contrast Agent for Magnetic Resonance Imaging

Recently, a growing interest has been seen in the development of T(1)–T(2) dual-mode probes that can simultaneously enhance contrast on T(1)- and T(2)-weighted images. A common strategy is to integrate T(1) and T(2) components in a decoupled manner into a nanoscale particle. This approach, however, often requires a multi-step synthesis and delicate nanoengineering, which may potentially affect the production and wide application of the probes. We herein report the facile synthesis of a 50-nm nanoscale metal–organic framework (NMOF) comprising gadolinium (Gd(3+)) and europium (Eu(3+)) as metallic nodes. These nanoparticles can be prepared in large quantities and can be easily coated with a layer of silica. The yielded Eu,Gd-NMOF@SiO(2) nanoparticles are less toxic, highly fluorescent, and afford high longitudinal (38 mM(−1)s(−1)) and transversal (222 mM(−1)s(−1)) relaxivities on a 7 T magnet. The nanoparticles were conjugated with c(RGDyK), a tumor-targeting peptide sequence, which has a high binding affinity toward integrin α(v)β(3). Eu,Gd-NMOF@SiO(2) nanoparticles, when intratumorally or intravenously injected, induce simultaneous signal enhancement and signal attenuation on T(1)-and T(2)-weighted images, respectively. These results suggest great potential of the NMOFs as a novel T(1)–T(2) dual-mode contrast agent.